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Question on Fiber

Posted on 2004-09-03
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Last Modified: 2010-04-17
At work, we have all of our switches connected via fiber. (2950g cisco switches I think).

Since we are connecting the switches via fiber, would this still be considered an ethernet LAN?  Or would it be considered a hybrid of ethernet and FDDI?

Also, what is up with this single and multi-mode stuff?

Thanks
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Question by:dissolved
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by:lrmoore
ID: 11977731
Fiber is just a layer 1 conductor. The end point electronics and protocols determine if it is Ethernet or FDDI. Your's are most definately Ethernet and not FDDI.
It is still a pure Ethernet LAN.

Single-mode and multi-mode differ in the size of the actual fiber inside, and the light source driver.
Single mode is much smaller diameter and is driven by laser lights (more expensive, long distance)
Multi-mode is bigger diameter and is driven by LED's (cheaper, shorter distance)

http://www.fiber-optics.info/articles/fiber-types.htm

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by:dissolved
ID: 11977794
So you're saying the trunked links of fiber are just layer 1 in this case. It's not FDDI because we are not running any FDDI protocols etc...

How is the fiber configured? I'm assuming through the switch?   What would I need to run fibers in between my switches at home? Just one fiber strand?
Thanks for link
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by:lrmoore
ID: 11977872
>It's not FDDI because we are not running any FDDI protocols etc...
Correct. FDDI is a layer 2 transport and you would need a bridge or router just like between Ethernet and frame-relay, or Ethernet and ATM.

The fiber is not really configured. You have 1 Transmit and 1 receive at each end (pair of strands, not single).
There is really nothing to configure on the switchport. You probably have GBIC's that slide into the Gigabit slots. You purchase the appropriate GBIC depending on the application. Different part numbers for multi-mode or single mode, or copper. It's just another Gigabit Ethernet port to the switch.

Do you have fiber ports on your switches, or do you have a slot? Which switches do you have?


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by:mikebernhardt
ID: 11977884
The fiber is just a wire that carries light instead of electricity. The electrical or light-carrying specifications are Layer 1. FDDI, ethernet, token ring, etc. are all Layer 2 specifications.

For ethernet, each strand of fiber is like a copper pair on a cat-5, so you need 2 of them for an ethernet connection. Going switch to switch, you cross them over just like with copper pairs. In your home you would use multimode-- single mode won't even work with distances that short.

The equipment on the end is all that matters for configuration. You either need compatible switch ports, or copper ports and media converters to go from copper to fiber. The ports or converters need to be multimode also to be compatible with your fiber.
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by:lrmoore
ID: 11977886
You'll have to get the right fiber jumper with the correct end terminations. There are multiple types and combinations.
If you still have a 2924c, then I think you have a 100Mb fiber connection that uses ST (Standard Twist) connectors, and if you have a 2950 with a GBIC slot, you'll have to purchase a WS-G5484 Short-Wavelengh GBIC (multi-mode). This GBIC has SC (Standard Click) type connectors. You could get yourself a jumper with SC on one and and ST on the other.
However, you can physically connect these two switches together, but since one is 100M only and the other is 1GB only, you can't "connect" them using fiber..
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by:mikebernhardt
ID: 11977887
Oops, I took so long to post that I crossed over lrmoore's reply...
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by:dissolved
ID: 11977899
I have fiber ports on my switches. Both 2924XL switches. So I will use one port on each switch to transmit, and the other port on each switch to receive?

Also, I was aware that you needed a router to connect different topologies (ethernet, frame relay etc). How can a bridge do this? Isnt a bridge just a device similar to a switch (but not as intelligent)?

Thanks man
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by:mikebernhardt
mikebernhardt earned 100 total points
ID: 11977907
I mean replies...

You might think about the cost vs. benefit here, although mine is not to question why. Fiber won't gain you anything over copper in your home unless you have a need for Gigabit Ethernet, and the parts are a lot more expensive.
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lrmoore earned 400 total points
ID: 11977944
For 2924cXL switches, your fiber ports are ST connectors. One is Tx and one is Rx. Connect the Tx on one to the Rx on the other and vice versa.
Here's the patch cable you need:
http://www.l-com.com/jump.jsp?lGen=productleader&itemID=468&itemType=PRODUCTLEADER&iMainCat=36&iSubCat=139&iSubSubCat=141&iProductID=468


Yes, a router is normally required to do the translation between topologies, some devices with both FDDI and Ethernet ports have the translational bridging capabilities inherent in the switch itself.


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by:lrmoore
ID: 11977948
You can use EITHER the 50/125 or the 62.5/125

 
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